This invention relates to sulfur-absorbent compositions, the manufacture of sulfur absorbents and their use.
The removal of sulfur from fluid streams can be desirable or necessary for a variety of reasons. If the fluid stream is to be released as a waste stream, removal of sulfur from the fluid stream can be necessary to meet the sulfur emission requirements set by various air pollution control authorities. Such requirements are generally in the range of about 10 ppm to 500 ppm of sulfur in the fluid stream. If the fluid stream is to be burned as a fuel, removal of sulfur from the fluid stream can be necessary to prevent environmental pollution. If the fluid stream is to be processed, removal of the sulfur is often necessary to prevent the poisoning of sulfur sensitive catalysts or to satisfy other process requirements.
Various absorption compositions have been used to remove sulfur from fluid streams when the sulfur is present as hydrogen sulfide. These absorption compositions can be manufactured by a variety of methods which include, for example, extrusion production techniques. A problem that is often encountered in the production of these absorption compositions is equipment wear caused by the abrasive nature of the absorption materials being manufactured. In certain attempts to produce commercial quantities of absorbent compositions, excessive equipment wear and downtime caused by the abrasive characteristics of the absorption material components have, in effect, rendered the production commercially unviable.
It is desirable for an absorbent composition to not only have a high sulfur-absorption capacity but also to have sufficient mechanical strength to permit its use as a contact material that is placed as an absorbent bed within a contact vessel. A low mechanical strength or low crush strength of an absorbent agglomerate can lead to excessive attrition thereby causing undesirable operating difficulties in commercial processes which utilize such absorbent agglomerates.
A further property of which it is desirable for absorption compositions to have is the ability to absorb large quantities of sulfur. This capability to absorb large amounts and maintain high concentrations of sulfur is sometimes referred to as xe2x80x9csulfur loadingxe2x80x9d and is generally reported in terms of percent sulfur loading. The term xe2x80x9cpercent sulfur loadingxe2x80x9d is generally defined as the parts by weight of sulfur absorbed upon the surface or within the pores of an absorption composition per parts by weight of the total absorbent composition multiplied by a factor of 100. It is desirable to have an absorption composition with the largest possible sulfur loading capacity.
An additional property desirable for an absorption composition is the ability to be regenerated to its original absorbing composition state after the absorbing composition has become spent. An absorbing composition generally becomes spent when its sulfur loading capacity has essentially been used up. It is desirable for the absorbing composition to be able to undergo numerous regeneration cycles without losing its sulfur loading capacity and other desirable properties.
Even though many absorbing compositions can effectively absorb hydrogen sulfide from fluid streams containing hydrogen sulfide, it is not uncommon for many of these absorbing compositions to effectively oxidize significant amounts of hydrogen sulfide to sulfur dioxide when contacted with such fluid streams. The resulting sulfur dioxide is not removed from the fluid stream by the absorbent composition and thus passes through the absorbent material with the contacted fluid stream. This phenomena is sometimes called xe2x80x9csulfur slippagexe2x80x9d. It is desirable to have an absorption material that has a high capacity to absorb sulfur from a fluid stream but which minimizes the amount of sulfur slippage.
In some absorption compositions, the addition of a promoter compound can be used to allow for easier regeneration of the absorbing material.
It is, thus, an object of the present invention to provide an improved absorption composition capable of removing certain sulfur compounds from fluid streams.
Another object of this invention is to provide an absorption process for the removal of sulfur from fluid streams.
Yet another object of the present invention is to provide an absorption composition characterized by exceptional mechanical strength and an improved process for the production of such composition.
A still further object of this invention is to provide a method of manufacturing an absorption composition that minimizes equipment wear and that produces an absorption composition having a high mechanical strength.
In accordance with one aspect of this invention, there is provided a composition comprising zinc oxide, silica and a colloidal oxide solution. In accordance with another aspect of this invention, there is provided a method for preparing a high crush strength absorption composition comprising the step of spraying a colloidal oxide solution onto a homogeneous mixture comprising zinc oxide and silica during tumbling agglomeration to form an agglomerate. Another aspect of the present invention includes an absorption process wherein a fluid stream is contacted under absorption conditions with an absorption composition comprising zinc oxide, silica and a colloidal oxide solution.
Other objects, advantages and features of this invention will become apparent from a study of this disclosure, the appended claims and the drawings in which: